Beds such as those used in hospitals, other health care facilities and noninstitutional health care settings include a frame, a mattress supported by the frame, and may also employ a topper. A typical topper includes a fabric or fabric-like cover or ticking which bounds an interior volume. The cover has an interior surface which faces inwardly toward the interior volume and an exterior surface which faces outwardly toward the environment. The cover is customarily made of a vapor permeable hydrophilic material whose permeability or vapor transfer properties are substantially invariant with temperature.
One type of topper is a nonintegrated topper which may be installed on or removed from the mattress depending on the requirements of the bed occupant. Some mattresses include an integrated topper which is not readily removeable from the mattress.
One style of topper is a microclimate control topper, which may be of the nonintegrated or integrated type. During typical use of such a topper a stream of air flows through the interior volume of the topper generally from the foot end of the topper to the head end of the topper where the air is exhausted to atmosphere. When an occupant of the bed perspires on the topper the perspiration, which is mostly water, vaporizes and passes across the vapor permeable cover or ticking and into the airstream. The airstream carries the perspiration vapor (i.e. water vapor) out of the interior of the topper. As a result the topper counteracts any tendency for moisture to accumulate on the occupant's skin thereby enhancing occupant comfort and reducing the likelihood that the occupant will develop pressure ulcers.
As already noted the cover or ticking of the topper is customarily made of a hydrophilic, vapor permeable material so that perspiration vapor can readily migrate across the cover and into the airstream. The hydrophilic, vapor permeable properties of the topper are beneficial for withdrawing perspiration vapor. However when the topper is cleaned or sanitized with commonly used cleaning chemicals, these same properties can cause the cleaning chemicals to be absorbed, which causes degradation of the material. Materials which have lower vapor permeability may be more resistant to chemical degradation due to their lower liquid absorption characteristics, however a ticking made of such materials would have poorer perspiration vapor withdrawal capabilities than a ticking made of a material with higher vapor permeability. The designer is therefore faced with an undesirable tradeoff between cleanability and moisture vapor withdrawal capability.